See above for details of subject identification for enrollment. Eligible individuals will be invited to come in for a screening visit for the moxifloxacin study with a target enrollment of 40 in each genotype group. We plan to contact up to 266 individuals who are in the upper and lower quintiles of QT genotype score to come in for the screening visit. We anticipate inviting approximately 160 individuals for the screening visit, with a goal enrollment sample size of 80 individuals. These subjects will be contacted by phone about participation in this study, and then informed consent will be obtained on arrival for the screening visit, and verified at subsequent visits if they are eligible for the study protocol.